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The problem can only be understood and addressed by drawing upon the resources of multidisciplinary approaches. Essential amino acids are often added to the diet in purified form eg, DL -methionine and L -lysine to minimize the total protein level as well as the cost of the diet. University of California Press. Many elements are required in trace amounts, usually because they play a catalytic role in enzymes. If your cat refuses to eat a therapeutic diet, your vet can give you a potassium supplement instead, if appropriate; some cats need a potassium supplement whether or not they eat the therapeutic kidney diet. These nutrients are discussed in this section.

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The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane.

It also harbors many nerve endings that provide the sense of touch and heat. It contains the hair follicles , sweat glands , sebaceous glands , apocrine glands , lymphatic vessels and blood vessels. The blood vessels in the dermis provide nourishment and waste removal from its own cells as well as from the Stratum basale of the epidermis. The dermis is structurally divided into two areas: The papillary region is composed of loose areolar connective tissue.

It is named for its fingerlike projections called papillae , that extend toward the epidermis. The papillae provide the dermis with a "bumpy" surface that interdigitates with the epidermis, strengthening the connection between the two layers of skin. In the palms, fingers, soles, and toes, the influence of the papillae projecting into the epidermis forms contours in the skin's surface.

These epidermal ridges occur in patterns see: The reticular region lies deep in the papillary region and is usually much thicker. It is composed of dense irregular connective tissue, and receives its name from the dense concentration of collagenous , elastic , and reticular fibers that weave throughout it.

These protein fibers give the dermis its properties of strength, extensibility, and elasticity. Also located within the reticular region are the roots of the hairs , sebaceous glands , sweat glands , receptors , nails , and blood vessels.

Tattoo ink is held in the dermis. Stretch marks often from pregnancy and obesity , are also located in the dermis. The subcutaneous tissue also hypodermis and subcutis is not part of the skin, and lies below the dermis of the cutis.

Its purpose is to attach the skin to underlying bone and muscle as well as supplying it with blood vessels and nerves. It consists of loose connective tissue, adipose tissue and elastin.

Fat serves as padding and insulation for the body. Human skin shows high skin color variety from the darkest brown to the lightest pinkish-white hues. Human skin shows higher variation in color than any other single mammalian species and is the result of natural selection. Skin pigmentation in humans evolved to primarily regulate the amount of ultraviolet radiation UVR penetrating the skin, controlling its biochemical effects.

The actual skin color of different humans is affected by many substances, although the single most important substance determining human skin color is the pigment melanin. Melanin is produced within the skin in cells called melanocytes and it is the main determinant of the skin color of darker-skinned humans. The skin color of people with light skin is determined mainly by the bluish-white connective tissue under the dermis and by the hemoglobin circulating in the veins of the dermis.

The red color underlying the skin becomes more visible, especially in the face, when, as consequence of physical exercise or the stimulation of the nervous system anger, fear , arterioles dilate.

There are at least five different pigments that determine the color of the skin. There is a correlation between the geographic distribution of UV radiation UVR and the distribution of indigenous skin pigmentation around the world.

Areas that highlight higher amounts of UVR reflect darker-skinned populations, generally located nearer towards the equator. Areas that are far from the tropics and closer to the poles have lower concentration of UVR, which is reflected in lighter-skinned populations.

In the same population it has been observed that adult human females are considerably lighter in skin pigmentation than males. Females need more calcium during pregnancy and lactation , and vitamin D which is synthesized from sunlight helps in absorbing calcium. For this reason it is thought that females may have evolved to have lighter skin in order to help their bodies absorb more calcium. The Fitzpatrick scale [22] [23] is a numerical classification schema for human skin color developed in as a way to classify the typical response of different types of skin to ultraviolet UV light:.

As skin ages, it becomes thinner and more easily damaged. Intensifying this effect is the decreasing ability of skin to heal itself as a person ages. Among other things, skin aging is noted by a decrease in volume and elasticity. There are many internal and external causes to skin aging. For example, aging skin receives less blood flow and lower glandular activity. A validated comprehensive grading scale has categorized the clinical findings of skin aging as laxity sagging , rhytids wrinkles , and the various facets of photoaging, including erythema redness , and telangiectasia , dyspigmentation brown discoloration , solar elastosis yellowing , keratoses abnormal growths and poor texture.

Cortisol causes degradation of collagen , [25] accelerating skin aging. Anti-aging supplements are used to treat skin aging. Photoaging has two main concerns: In younger skin, sun damage will heal faster since the cells in the epidermis have a faster turnover rate, while in the older population the skin becomes thinner and the epidermis turnover rate for cell repair is lower which may result in the dermis layer being damaged. The human skin is a rich environment for microbes.

Most come from only four phyla: Propionibacteria and Staphylococci species were the main species in sebaceous areas. There are three main ecological areas: In moist places on the body Corynebacteria together with Staphylococci dominate.

In dry areas, there is a mixture of species but dominated by b- Proteobacteria and Flavobacteriales. Ecologically, sebaceous areas had greater species richness than moist and dry ones. The areas with least similarity between people in species were the spaces between fingers , the spaces between toes , axillae , and umbilical cord stump. Most similarly were beside the nostril , nares inside the nostril , and on the back. Reflecting upon the diversity of the human skin researchers on the human skin microbiome have observed: The NIH has launched the Human Microbiome Project to characterize the human microbiota which includes that on the skin and the role of this microbiome in health and disease.

Microorganisms like Staphylococcus epidermidis colonize the skin surface. The density of skin flora depends on region of the skin. The disinfected skin surface gets recolonized from bacteria residing in the deeper areas of the hair follicle, gut and urogenital openings. Diseases of the skin include skin infections and skin neoplasms including skin cancer. Dermatology is the branch of medicine that deals with conditions of the skin. The skin supports its own ecosystems of microorganisms , including yeasts and bacteria, which cannot be removed by any amount of cleaning.

Estimates place the number of individual bacteria on the surface of one square inch 6. Oily surfaces, such as the face, may contain over million bacteria per square inch 6.

Despite these vast quantities, all of the bacteria found on the skin's surface would fit into a volume the size of a pea. When the balance is disturbed, there may be an overgrowth and infection, such as when antibiotics kill microbes , resulting in an overgrowth of yeast. The skin is continuous with the inner epithelial lining of the body at the orifices, each of which supports its own complement of microbes. Cosmetics should be used carefully on the skin because these may cause allergic reactions.

Each season requires suitable clothing in order to facilitate the evaporation of the sweat. Sunlight, water and air play an important role in keeping the skin healthy. Oily skin is caused by over-active sebaceous glands, that produce a substance called sebum , a naturally healthy skin lubricant. Oily skin is typified by shininess, blemishes and pimples.

The negative aspect of the oily-skin type is that oily complexions are especially susceptible to clogged pores, blackheads , and buildup of dead skin cells on the surface of the skin. Human skin has a low permeability ; that is, most foreign substances are unable to penetrate and diffuse through the skin.

Skin's outermost layer, the stratum corneum, is an effective barrier to most inorganic nanosized particles. However, in some cases it is desirable to allow particles entry to the body through the skin. Potential medical applications of such particle transfer has prompted developments in nanomedicine and biology to increase skin permeability.

One application of transcutaneous particle delivery could be to locate and treat cancer. Nanomedical researchers seek to target the epidermis and other layers of active cell division where nanoparticles can interact directly with cells that have lost their growth-control mechanisms cancer cells. Such direct interaction could be used to more accurately diagnose properties of specific tumors or to treat them by delivering drugs with cellular specificity.

The permeability of skin relative to different shapes of nanoparticles has also been studied. Research has shown that spherical particles have a better ability to penetrate the skin compared to oblong ellipsoidal particles because spheres are symmetric in all three spatial dimensions.

Titanium oxide TiO2 , zinc oxide ZnO , and silver nanoparticles are ineffective in penetrating the skin past the stratum corneum. Because CdSe is toxic to living organisms, the particle must be covered in a surface group. An experiment comparing the permeability of quantum dots coated in polyethylene glycol PEG , PEG- amine , and carboxylic acid concluded the PEG and PEG-amine surface groups allowed for the greatest penetration of particles.

The carboxylic acid coated particles did not penetrate past the stratum corneum. Scientists previously believed that the skin was an effective barrier to inorganic particles.

Damage from mechanical stressors was believed to be the only way to increase its permeability. For example, ultraviolet radiation UVR has been used to slightly damage the surface of skin, causing a time-dependent defect allowing easier penetration of nanoparticles. When the TEWL reaches its highest value, the maximum density of nanoparticles is able to permeate the skin. Studies confirm that UVR damaged skin significantly increases the permeability.

However, the specific permeability of skin after UVR exposure relative to particles of different sizes and materials has not been determined. Other skin damaging methods used to increase nanoparticle penetration include tape stripping, skin abrasion , and chemical enhancement. Tape stripping is the process in which tape is applied to skin then lifted to remove the top layer of skin. Skin abrasion is done by shaving the top micrometers off the surface of the skin.

Chemical enhancement is the process in which chemicals such as polyvinylpyrrolidone PVP , dimethyl sulfoxide DMSO , and oleic acid are applied to the surface of the skin to increase permeability. Electroporation is the application of short pulses of electric fields on skin and has proven to increase skin permeability.

The pulses are high voltage and on the order of milliseconds when applied. Charged molecules penetrate the skin more frequently than neutral molecules after the skin has been exposed to electric field pulses.

Results have shown molecules on the order of micrometers to easily permeate electroporated skin. A large area of interest in nanomedicine is the transdermal patch because of the possibility of a painless application of therapeutic agents with very few side effects. Transdermal patches have been limited to administer a small number of drugs, such as nicotine , because of the limitations in permeability of the skin. Development of techniques that increase skin permeability has led to more drugs that can be applied via transdermal patches and more options for patients.

Increasing the permeability of skin allows nanoparticles to penetrate and target cancer cells. Nanoparticles along with multi-modal imaging techniques have been used as a way to diagnose cancer non-invasively. Skin with high permeability allowed quantum dots with an antibody attached to the surface for active targeting to successfully penetrate and identify cancerous tumors in mice.

The states are made up of pairs of attributes hot and moist, cold and moist, hot and dry, and cold and dry , which are made of four humours: Galen thought that for a person to have gout , kidney stones , or arthritis was scandalous, which Gratzer likens to Samuel Butler's Erehwon where sickness is a crime. In the s, Paracelsus was probably the first to criticize Galen publicly. Leonardo did not publish his works on this subject, but he was not afraid of thinking for himself and he definitely disagreed with Galen.

Jan Baptist van Helmont , who discovered several gases such as carbon dioxide , performed the first quantitative experiment. Robert Boyle advanced chemistry. Sanctorius measured body weight. Physician Herman Boerhaave modeled the digestive process. Physiologist Albrecht von Haller worked out the difference between nerves and muscles. Sometimes forgotten during his life, James Lind , a physician in the British navy, performed the first scientific nutrition experiment in Lind discovered that lime juice saved sailors that had been at sea for years from scurvy , a deadly and painful bleeding disorder.

Between and , an estimated two million sailors had died of scurvy. Around , Antoine Lavoisier discovered the details of metabolism, demonstrating that the oxidation of food is the source of body heat. Called the most fundamental chemical discovery of the 18th century, [30] Lavoisier discovered the principle of conservation of mass. His ideas made the phlogiston theory of combustion obsolete. In , George Fordyce recognized calcium as necessary for the survival of fowl.

In the early 19th century, the elements carbon , nitrogen , hydrogen , and oxygen were recognized as the primary components of food, and methods to measure their proportions were developed. In , François Magendie discovered that dogs fed only carbohydrates sugar , fat olive oil , and water died evidently of starvation, but dogs also fed protein survived, identifying protein as an essential dietary component. In the early s, Kanehiro Takaki observed that Japanese sailors whose diets consisted almost entirely of white rice developed beriberi or endemic neuritis, a disease causing heart problems and paralysis , but British sailors and Japanese naval officers did not.

Adding various types of vegetables and meats to the diets of Japanese sailors prevented the disease, not because of the increased protein as Takaki supposed but because it introduced a few parts per million of thiamine to the diet, later understood as a cure [39]. In , Eugen Baumann observed iodine in thyroid glands.

In , Christiaan Eijkman worked with natives of Java , who also suffered from beriberi. Eijkman observed that chickens fed the native diet of white rice developed the symptoms of beriberi but remained healthy when fed unprocessed brown rice with the outer bran intact.

His assistant, Gerrit Grijns correctly identified and described the anti-beriberi substance in rice. Eijkman cured the natives by feeding them brown rice, discovering that food can cure disease. Over two decades later, nutritionists learned that the outer rice bran contains vitamin B1, also known as thiamine. In the early 20th century, Carl von Voit and Max Rubner independently measured caloric energy expenditure in different species of animals, applying principles of physics in nutrition. In , Edith G.

Willcock and Frederick Hopkins showed that the amino acid tryptophan aids the well-being of mice but it did not assure their growth. Babcock and Edwin B. Hart started the cow feeding, single-grain experiment , which took nearly four years to complete.

In , Casimir Funk coined the term vitamin , a vital factor in the diet, from the words "vital" and "amine," because these unknown substances preventing scurvy, beriberi, and pellagra , were thought then to be derived from ammonia.

The vitamins were studied in the first half of the 20th century. In , Elmer McCollum and Marguerite Davis discovered the first vitamin, fat-soluble vitamin A , then water-soluble vitamin B in ; now known to be a complex of several water-soluble vitamins and named vitamin C as the then-unknown substance preventing scurvy. In , Sir Edward Mellanby incorrectly identified rickets as a vitamin A deficiency because he could cure it in dogs with cod liver oil.

Bishop discover vitamin E as essential for rat pregnancy, originally calling it "food factor X" until In , Hart discovered that trace amounts of copper are necessary for iron absorption. In , Albert Szent-Györgyi isolated ascorbic acid , and in proved that it is vitamin C by preventing scurvy.

In , he synthesized it, and in , he won a Nobel Prize for his efforts. Szent-Györgyi concurrently elucidated much of the citric acid cycle. In the s, William Cumming Rose identified essential amino acids , necessary protein components that the body cannot synthesize.

In , Underwood and Marston independently discovered the necessity of cobalt. In , Eugene Floyd DuBois showed that work and school performance are related to caloric intake. In , Erhard Fernholz discovered the chemical structure of vitamin E and then he tragically disappeared.

In , rationing in the United Kingdom during and after World War II took place according to nutritional principles drawn up by Elsie Widdowson and others. In , The U. Department of Agriculture introduced the Food Guide Pyramid. The list of nutrients that people are known to require is, in the words of Marion Nestle , "almost certainly incomplete".

Some nutrients can be stored - the fat-soluble vitamins - while others are required more or less continuously. Poor health can be caused by a lack of required nutrients, or for some vitamins and minerals, too much of a required nutrient. The macronutrients are carbohydrates , fiber , fats , protein , and water. Some of the structural material can be used to generate energy internally, and in either case it is measured in Joules or kilocalories often called "Calories" and written with a capital C to distinguish them from little 'c' calories.

Vitamins, minerals, fiber, and water do not provide energy, but are required for other reasons. Molecules of carbohydrates and fats consist of carbon, hydrogen, and oxygen atoms.

Carbohydrates range from simple monosaccharides glucose, fructose and galactose to complex polysaccharides starch. Fats are triglycerides , made of assorted fatty acid monomers bound to a glycerol backbone. Some fatty acids, but not all, are essential in the diet: Protein molecules contain nitrogen atoms in addition to carbon, oxygen, and hydrogen.

The fundamental components of protein are nitrogen-containing amino acids , some of which are essential in the sense that humans cannot make them internally. Some of the amino acids are convertible with the expenditure of energy to glucose and can be used for energy production, just as ordinary glucose, in a process known as gluconeogenesis.

By breaking down existing protein, the carbon skeleton of the various amino acids can be metabolized to intermediates in cellular respiration; the remaining ammonia is discarded primarily as urea in urine. Carbohydrates may be classified as monosaccharides , disaccharides , or polysaccharides depending on the number of monomer sugar units they contain.

They constitute a large part of foods such as rice , noodles , bread , and other grain -based products, also potatoes , yams, beans, fruits, fruit juices and vegetables. Monosaccharides, disaccharides, and polysaccharides contain one, two, and three or more sugar units, respectively.

Polysaccharides are often referred to as complex carbohydrates because they are typically long, multiple branched chains of sugar units. Traditionally, simple carbohydrates are believed to be absorbed quickly, and therefore to raise blood-glucose levels more rapidly than complex carbohydrates.

This, however, is not accurate. Dietary fiber is a carbohydrate that is incompletely absorbed in humans and in some animals. Like all carbohydrates, when it is metabolized it can produce four Calories kilocalories of energy per gram. However, in most circumstances it accounts for less than that because of its limited absorption and digestibility. Dietary fiber consists mainly of cellulose, a large carbohydrate polymer which is indigestible as humans do not have the required enzymes to disassemble it.

There are two subcategories: Whole grains, fruits especially plums , prunes , and figs , and vegetables are good sources of dietary fiber. There are many health benefits of a high-fiber diet. Dietary fiber helps reduce the chance of gastrointestinal problems such as constipation and diarrhea by increasing the weight and size of stool and softening it. Insoluble fiber, found in whole wheat flour , nuts and vegetables, especially stimulates peristalsis ;— the rhythmic muscular contractions of the intestines, which move digest along the digestive tract.

Soluble fiber, found in oats, peas, beans, and many fruits, dissolves in water in the intestinal tract to produce a gel that slows the movement of food through the intestines. This may help lower blood glucose levels because it can slow the absorption of sugar. Additionally, fiber, perhaps especially that from whole grains, is thought to possibly help lessen insulin spikes, and therefore reduce the risk of type 2 diabetes.

The link between increased fiber consumption and a decreased risk of colorectal cancer is still uncertain. A molecule of dietary fat typically consists of several fatty acids containing long chains of carbon and hydrogen atoms , bonded to a glycerol.

They are typically found as triglycerides three fatty acids attached to one glycerol backbone. Fats may be classified as saturated or unsaturated depending on the detailed structure of the fatty acids involved.

Saturated fats have all of the carbon atoms in their fatty acid chains bonded to hydrogen atoms, whereas unsaturated fats have some of these carbon atoms double-bonded , so their molecules have relatively fewer hydrogen atoms than a saturated fatty acid of the same length. Unsaturated fats may be further classified as monounsaturated one double-bond or polyunsaturated many double-bonds. Furthermore, depending on the location of the double-bond in the fatty acid chain, unsaturated fatty acids are classified as omega-3 or omega-6 fatty acids.

Trans fats are a type of unsaturated fat with trans -isomer bonds; these are rare in nature and in foods from natural sources; they are typically created in an industrial process called partial hydrogenation.

There are nine kilocalories in each gram of fat. Fatty acids such as conjugated linoleic acid , catalpic acid, eleostearic acid and punicic acid , in addition to providing energy, represent potent immune modulatory molecules. Saturated fats typically from animal sources have been a staple in many world cultures for millennia.

Saturated and some trans fats are typically solid at room temperature such as butter or lard , while unsaturated fats are typically liquids such as olive oil or flaxseed oil. Trans fats are very rare in nature, and have been shown to be highly detrimental to human health, but have properties useful in the food processing industry, such as rancidity resistance. Most fatty acids are non-essential, meaning the body can produce them as needed, generally from other fatty acids and always by expending energy to do so.

However, in humans, at least two fatty acids are essential and must be included in the diet. An appropriate balance of essential fatty acids— omega-3 and omega-6 fatty acids —seems also important for health, although definitive experimental demonstration has been elusive.

Both of these "omega" long-chain polyunsaturated fatty acids are substrates for a class of eicosanoids known as prostaglandins , which have roles throughout the human body.

They are hormones , in some respects. The omega-3 eicosapentaenoic acid EPA , which can be made in the human body from the omega-3 essential fatty acid alpha-linolenic acid ALA , or taken in through marine food sources, serves as a building block for series 3 prostaglandins e.

The omega-6 dihomo-gamma-linolenic acid DGLA serves as a building block for series 1 prostaglandins e. An appropriately balanced intake of omega-3 and omega-6 partly determines the relative production of different prostaglandins, which is one reason why a balance between omega-3 and omega-6 is believed important for cardiovascular health.

In industrialized societies, people typically consume large amounts of processed vegetable oils, which have reduced amounts of the essential fatty acids along with too much of omega-6 fatty acids relative to omega-3 fatty acids. Moreover, the conversion desaturation of DGLA to AA is controlled by the enzyme deltadesaturase , which in turn is controlled by hormones such as insulin up-regulation and glucagon down-regulation. The amount and type of carbohydrates consumed, along with some types of amino acid, can influence processes involving insulin, glucagon, and other hormones; therefore, the ratio of omega-3 versus omega-6 has wide effects on general health, and specific effects on immune function and inflammation , and mitosis i.

Proteins are structural materials in much of the animal body e. They also form the enzymes that control chemical reactions throughout the body.

Each protein molecule is composed of amino acids , which are characterized by inclusion of nitrogen and sometimes sulphur these components are responsible for the distinctive smell of burning protein, such as the keratin in hair.

The body requires amino acids to produce new proteins protein retention and to replace damaged proteins maintenance. As there is no protein or amino acid storage provision, amino acids must be present in the diet.

Excess amino acids are discarded, typically in the urine. For all animals, some amino acids are essential an animal cannot produce them internally and some are non-essential the animal can produce them from other nitrogen-containing compounds. About twenty amino acids are found in the human body, and about ten of these are essential and, therefore, must be included in the diet.

A diet that contains adequate amounts of amino acids especially those that are essential is particularly important in some situations: A complete protein source contains all the essential amino acids; an incomplete protein source lacks one or more of the essential amino acids. It is possible with protein combinations of two incomplete protein sources e.

However, complementary sources of protein do not need to be eaten at the same meal to be used together by the body. Water is excreted from the body in multiple forms; including urine and feces , sweating , and by water vapour in the exhaled breath.

Therefore, it is necessary to adequately rehydrate to replace lost fluids. Early recommendations for the quantity of water required for maintenance of good health suggested that 6—8 glasses of water daily is the minimum to maintain proper hydration. Most of this quantity is contained in prepared foods. For healthful hydration, the current EFSA guidelines recommend total water intakes of 2.

These reference values include water from drinking water, other beverages, and from food. The EFSA panel also determined intakes for different populations. Recommended intake volumes in the elderly are the same as for adults as despite lower energy consumption, the water requirement of this group is increased due to a reduction in renal concentrating capacity.

Dehydration and over-hydration - too little and too much water, respectively - can have harmful consequences. Drinking too much water is one of the possible causes of hyponatremia , i. Pure ethanol provides 7 calories per gram. For distilled spirits , a standard serving in the United States is 1.

A 5 ounce serving of wine contains to calories. A 12 ounce serving of beer contains 95 to calories. Alcoholic beverages are considered empty calorie foods because other than calories, these contribute no essential nutrients.

The micronutrients are minerals , vitamins , and others. Dietary minerals are inorganic chemical elements required by living organisms, [70] other than the four elements carbon , hydrogen , nitrogen , and oxygen that are present in nearly all organic molecules.

The term "mineral" is archaic, since the intent is to describe simply the less common elements in the diet.

Some are heavier than the four just mentioned, including several metals , which often occur as ions in the body. Some dietitians recommend that these be supplied from foods in which they occur naturally, or at least as complex compounds, or sometimes even from natural inorganic sources such as calcium carbonate from ground oyster shells. Some minerals are absorbed much more readily in the ionic forms found in such sources. On the other hand, minerals are often artificially added to the diet as supplements; the most famous is likely iodine in iodized salt which prevents goiter.

Many elements are essential in relative quantity; they are usually called "bulk minerals". Some are structural, but many play a role as electrolytes. Many elements are required in trace amounts, usually because they play a catalytic role in enzymes. Vitamins are essential nutrients, [70] necessary in the diet for good health.

Vitamin D is an exception, as it can be synthesized in the skin in the presence of UVB radiation , and many animal species can synthesize vitamin C. Vitamin deficiencies may result in disease conditions, including goitre , scurvy , osteoporosis , impaired immune system, disorders of cell metabolism, certain forms of cancer, symptoms of premature aging, and poor psychological health , among many others.

Phytochemicals such as polyphenols are compounds produced naturally in plants phyto means "plant" in Greek. In general, the term is used to refer to compounds which do not appear to be nutritionally essential and yet may have positive impacts on health.

To date, there is no conclusive evidence in humans that polyphenols or other non-nutrient compounds from plants have health benefit effects.

While initial studies sought to reveal if nutrient antioxidant supplements might promote health, one meta-analysis concluded that supplementation with vitamins A and E and beta-carotene did not convey any benefits and may in fact increase risk of death. Vitamin C and selenium supplements did not impact mortality rate. Health effects of non-nutrient phytochemicals such as polyphenols were not assessed in this review.

Animal intestines contain a large population of gut flora. In humans, the four dominant phyla are Firmicutes , Bacteroidetes , Actinobacteria , and Proteobacteria. Bacteria in the large intestine perform many important functions for humans, including breaking down and aiding in the absorption of fermentable fiber, stimulating cell growth, repressing the growth of harmful bacteria, training the immune system to respond only to pathogens, producing vitamin B 12 , and defending against some infectious diseases.

There is not yet a scientific consensus as to health benefits accruing from probiotics or prebiotics. Carnivore and herbivore diets are contrasting, with basic nitrogen and carbon proportions vary for their particular foods.

Many herbivores rely on bacterial fermentation to create digestible nutrients from indigestible plant cellulose, while obligate carnivores must eat animal meats to obtain certain vitamins or nutrients their bodies cannot otherwise synthesize. Plant nutrition is the study of the chemical elements that are necessary for plant growth. Some elements are directly involved in plant metabolism. However, this principle does not account for the so-called beneficial elements, whose presence, while not required, has clear positive effects on plant growth.

A nutrient that is able to limit plant growth according to Liebig's law of the minimum is considered an essential plant nutrient if the plant cannot complete its full life cycle without it. There are 16 essential plant soil nutrients, besides the three major elemental nutrients carbon and oxygen that are obtained by photosynthetic plants from carbon dioxide in air, and hydrogen , which is obtained from water. Plants uptake essential elements from the soil through their roots and from the air consisting of mainly nitrogen and oxygen through their leaves.

Green plants obtain their carbohydrate supply from the carbon dioxide in the air by the process of photosynthesis. Carbon and oxygen are absorbed from the air, while other nutrients are absorbed from the soil. These hydrogen ions displace cations attached to negatively charged soil particles so that the cations are available for uptake by the root.

In the leaves, stomata open to take in carbon dioxide and expel oxygen. The carbon dioxide molecules are used as the carbon source in photosynthesis. Although nitrogen is plentiful in the Earth's atmosphere, very few plants can use this directly. Most plants, therefore, require nitrogen compounds to be present in the soil in which they grow. This is made possible by the fact that largely inert atmospheric nitrogen is changed in a nitrogen fixation process to biologically usable forms in the soil by bacteria.

Plant nutrition is a difficult subject to understand completely, partially because of the variation between different plants and even between different species or individuals of a given clone. Elements present at low levels may cause deficiency symptoms, and toxicity is possible at levels that are too high.

Furthermore, deficiency of one element may present as symptoms of toxicity from another element, and vice versa. Canada's Food Guide is an example of a government-run nutrition program. Produced by Health Canada , the guide advises food quantities, provides education on balanced nutrition, and promotes physical activity in accordance with government-mandated nutrient needs.

Like other nutrition programs around the world, Canada's Food Guide divides nutrition into four main food groups: Dietary and physical activity guidelines from the USDA are presented in the concept of MyPlate , which superseded the food pyramid , which replaced the Four Food Groups. Department of Health and Human Services provides a sample week-long menu that fulfills the nutritional recommendations of the government. Governmental organisations have been working on nutrition literacy interventions in non-primary health care settings to address the nutrition information problem in the U.

The FNP has developed a series of tools to help families participating in the Food Stamp Program stretch their food dollar and form healthful eating habits including nutrition education. It is designed to assist limited-resource audiences in acquiring the knowledge, skills, attitudes, and changed behavior necessary for nutritionally sound diets, and to contribute to their personal development and the improvement of the total family diet and nutritional well-being. Launched in , this program promotes lifelong healthful eating patterns and physically active lifestyles for children and their families.

It is an interactive educational program designed to help prevent childhood obesity through classroom activities that teach children healthful eating habits and physical exercise. Nutrition is taught in schools in many countries. In England and Wales , the Personal and Social Education and Food Technology curricula include nutrition, stressing the importance of a balanced diet and teaching how to read nutrition labels on packaging.

In many schools, a Nutrition class will fall within the Family and Consumer Science or Health departments. In some American schools, students are required to take a certain number of FCS or Health related classes. Nutrition is offered at many schools, and, if it is not a class of its own, nutrition is included in other FCS or Health classes such as: In many Nutrition classes, students learn about the food groups, the food pyramid, Daily Recommended Allowances, calories, vitamins, minerals, malnutrition, physical activity, healthful food choices, portion sizes, and how to live a healthy life.

In the US, Registered dietitian nutritionists RDs or RDNs [89] are health professionals qualified to provide safe, evidence-based dietary advice which includes a review of what is eaten, a thorough review of nutritional health, and a personalized nutritional treatment plan.

They also provide preventive and therapeutic programs at work places, schools and similar institutions. Certified Clinical Nutritionists or CCNs, are trained health professionals who also offer dietary advice on the role of nutrition in chronic disease, including possible prevention or remediation by addressing nutritional deficiencies before resorting to drugs. These Board Certified Nutritionists typically specialize in obesity and chronic disease.

In order to become board certified, potential CNS candidate must pass an examination, much like Registered Dieticians. This exam covers specific domains within the health sphere including; Clinical Intervention and Human Health.

The study found that health literacy increases with education and people living below the level of poverty have lower health literacy than those above it. Another study examining the health and nutrition literacy status of residents of the lower Mississippi Delta found that 52 percent of participants had a high likelihood of limited literacy skills.

For example, only 12 percent of study participants identified the My Pyramid graphic two years after it had been launched by the USDA. The study also found significant relationships between nutrition literacy and income level and nutrition literacy and educational attainment [93] further delineating priorities for the region.

Among these problems are the lack of information about food choices, a lack of understanding of nutritional information and its application to individual circumstances, limited or difficult access to healthful foods, and a range of cultural influences and socioeconomic constraints such as low levels of education and high levels of poverty that decrease opportunities for healthful eating and living.